SECT. I 



CRYPTOGAMS 



363 



complicated thallus, which is always, however, formed of branched filaments ; by 

 calcareous incrustation some forms come to resemble coral. Acetabularia mediter- 

 ranea (•''*) (Fig. 285) will serve as an example of such calcareous Algae. The thin 

 stalk of the thalhis is attached by means of rhizoids, while the umbrella-like disc 

 consists of closely united tubular outgrowths, each of which is to be regarded as 

 a gametangiuni. The contents of the latter do not form the biciliate gametes 



directly, but first divide into a large 

 number of firm-walled cysts. These 

 remain in the resting condition 

 throughout the winter, and then give 

 rise to numerous gametes which con- 

 jugate in pairs. The zygotes ger- 

 minate promptly and grow into new 

 plants. 



Order 5. Siphonales. — The Siph- 

 oneae are distinguished from the pre- 

 ceding groups of Algae by the struc- 

 ture of their thallus, which, although 

 more or less profusely branched, is not 



Fio. 284. — Voxtwn oi Cladophora glomerat a. (x4S.) 

 To tliR right a swarm-spore, (x 1000.) 



Fig. 285. — Acefuhiilaria meiliterranca. 

 (Nat. size.) 



at first divided by transverse septa. The cell wall thus encloses a continuous proto- 

 plasmic body in which numerous nuclei and small green chloroplasts are embedded. 

 The same type of thallus is also met with in the Phycomycetes or Algal Fungi. 



The majority of the Siphoneae inhabit the sea, and on account of the com- 

 plicated segmentation of their thallus, afford one of the most interesting types 

 of algal development. The genus Caulerpa (^^), represented by many species 

 iidiabiting the warmer water of the ocean, has a creeping main a.xis. Increasing 

 in length by apical growth, the s'lem-like portion of the thallus gives off from its 

 under surface profusely branched colourless rhizoids, while, from its upper side, 





